Compositions and methods including depositing nanomaterial

ABSTRACT

An ink composition comprising a nanomaterial and a liquid vehicle, wherein the liquid vehicle comprises a composition including one or more functional groups that are capable of being cross-linked is disclosed. An ink composition comprising a nanomaterial, a liquid vehicle, and scatterers is also disclosed. An ink composition comprising a nanomaterial and a liquid vehicle, wherein the liquid vehicle comprises a perfluorocompound is further disclosed. A method for inkjet printing an ink including nanomaterial and a liquid vehicle with a surface tension that is not greater than about 25 dyne/cm is disclosed. In certain preferred embodiments, the nanomaterial comprises semiconductor nanocrystals. Devices prepared from inks and methods of the invention are also described.

This application is a continuation application of U.S. patentapplication Ser. No. 12/655,074, filed 22 Dec. 2009, which is acontinuation application of commonly owned International Application No.PCT/US2008/007901, filed 25 Jun. 2008, which was published in theEnglish language as PCT Publication No. WO 2009/0014590 on 29 Jan. 2009.The PCT Application claims priority from commonly owned U.S. ApplicationNo. 60/946,090, filed 25 Jun. 2007, and U.S. Application No. 60/949,306,filed 12 Jul. 2007. The disclosures of each of the foregoingapplications are hereby incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to the technical field of nanomaterials,including but not limited to, compositions including a nonmaterial andmethods including depositing a nanomaterial or composition including ananomaterial.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop improvedcompositions and methods for depositing a nanomaterial. Such methods andcompositions are useful in fabricating devices and/or arrays of devices.

In accordance with one aspect of the invention, there is provided an inkcomposition comprising a nanomaterial and a liquid vehicle, wherein theliquid vehicle comprises a perfluorocompound. In certain most preferredembodiments, the liquid vehicle comprises Fluorinert FC-77, availablefrom 3M.

In certain aspects and embodiments of the invention described herein, ofan ink in accordance with the invention, the ink composition comprises adispersion. For certain applications, it is desirable for the dispersionto be colloidal.

In certain embodiment, the ink can further include scatterers.

In certain embodiments, the liquid vehicle comprises a perfluorocompoundincluding one or more functional groups that are capable of beingcross-linked. In certain embodiments, the functional units can becross-linked by UV treatment. In certain embodiments, the functionalunits can be cross-linked by thermal treatment. In certain embodiments,the functional units can be cross-linked by other cross-linkingtechnique readily ascertainable by a person of ordinary skill in arelevant art. In certain embodiments, the composition including one ormore functional groups that are capable of being cross-linked can be theliquid vehicle itself. In certain embodiments, it can be a co-solvent.In certain embodiments, it can be a component of a mixture with theliquid vehicle.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals. In certain preferred embodiments, the nanomaterialcomprises semiconductor nanocrystals at least a portion of which includea fluorinated ligand attached to a surface thereof.

In accordance with one aspect of the invention, there is provided an inkcomposition comprising a nanomaterial and a liquid vehicle, wherein theliquid vehicle comprises a composition including one or more functionalgroups that are capable of being cross-linked. In certain embodiments,the functional units can be cross-linked by UV treatment. In certainembodiments, the functional units can be cross-linked by thermaltreatment. In certain embodiments, the functional units can becross-linked by other cross-linking technique readily ascertainable by aperson of ordinary skill in a relevant art. In certain embodiments, thecomposition including one or more functional groups that are capable ofbeing cross-linked can be the liquid vehicle itself. In certainembodiments, it can be a co-solvent. In certain embodiments, it can be acomponent of a mixture with the liquid vehicle.

In certain embodiments, the ink can further include scatterers.

In accordance with another aspect of the invention, there is provided anink composition comprising a nanomaterial, a liquid vehicle, andscatterers.

Examples of scatterers (also referred to herein as scattering particles)include, without limitation, metal or metal oxide particles, airbubbles, and glass beads (solid or hollow). Other scatterers can bereadily identified by those of ordinary skill in the art. In certainembodiments, scatterers have a spherical shape. Preferred examples ofscattering particles include, but are not limited to, TiO₂, SiO₂,BaTiO₃, and ZnO. Selection of the size and size distribution of thescatterers is readily determinable by those of ordinary skill in theart. The size and size distribution is preferably based upon therefractive index mismatch of the scattering particle and the hostmaterial in which it the scatterer is to be dispersed after removal ofany liquid medium that may be present, and the preselected wavelength(s)to be scattered according to Rayleigh scattering theory. The surface ofthe scattering particle may further be treated to improve dispersabilityand stability in the host material. In one embodiment, the scatteringparticle comprises TiO₂ (R902+ from DuPont) of 0.2 μm particle size, ina concentration between 0.001% and 20% by weight. In certain preferredembodiments, the concentration range of the scatterers is between 0.1%and 10% by weight. In a certain more preferred embodiments, an inkincludes a scatterer comprising TiO₂ at a concentration in a range fromabout 1% to about 5% by weight.

In certain aspects and embodiments of the inventions described herein,it is not necessary to have the nanomaterial particles (e.g.,semiconductor nanocrystals) individually dispersed in the liquidvehicle. The nanomaterial particles (e.g., semiconductor nanocrystals)may be aggregated. In certain embodiments of the inventions describedherein, the nanomaterial particles (e.g., semiconductor nanocrystals)may be included within or adsorbed onto polymer particles. In certainembodiments of the inventions described herein, the nanomaterialparticles (e.g., semiconductor nanocrystals) may be included within oradsorbed onto a matrix. The matrix can be polymeric or non-polymeric.

In certain aspects and embodiments of the invention described herein,the nanomaterial comprises semiconductor nanocrystals.

Semiconductor nanocrystals possess characteristics and properties thatmake them particularly well-suited for use in a variety of devices andother end-use applications, including, but not limited to, lightemitting devices, displays, photodetectors, nonvolatile random memorydevices, solar cells, sensors, photovoltaic devices, etc.

In certain aspects and embodiments of the invention described herein,the nanomaterial comprises semiconductor nanocrystals wherein at least aportion of the semiconductor nanocrystals include one or more ligandsattached to a surface thereof.

In certain aspects and embodiments of the invention described herein, anink in accordance with an embodiment of the invention can furthercomprises a material capable of transporting charge. In certainembodiments, the material capable of transporting charge has a tripletenergy which is at least greater than the bandgap of the semiconductornanocrystals included in the ink. In certain embodiments, the materialcapable of transporting charge included in the ink is at least partiallysoluble in the liquid vehicle.

In certain aspects and embodiments of the invention described herein, anink in accordance with an embodiment of the invention can furtherinclude a variety of components such as those typically used in inkjetliquid vehicles and inks, such as, but not limited to solvents,cosolvents, surfactants, biocides, buffers, viscosity modifiers,sequestering agents, colorants, stabilizing agents, humectants, fillers,extenders, water, and mixtures thereof.

In accordance with another aspect of the invention, there is provided amethod for depositing an ink composition comprising a nanomaterial and aliquid vehicle having a surface tension less than about 25 dyne/cm. Incertain embodiments, the liquid vehicle has a surface tension no greaterthan about 15 dyne/cm. Examples of liquid vehicles having a surfacetension a vehicle less than about 25 dyne/cm include those in whichorganic materials typically used in fabricating various electronicdevices (e.g., light-emitting devices, photodetectors, and other devicesincluding semiconductor nanocrystals) are insoluble. Examples of suchliquid vehicles include fluorinated solvents, such as perfluorodecalin,or the Fluorinert series of solvents sold by 3M. In creating inks fromsuch solvents, the surface tension and viscosity may fall below thosenormally required for inkjet, e.g., 25 dyne/cm. Fluorinert FC-77, forexample, has a surface tension of 13 dyne/cm and a viscosity of 1.3 cP.

A method for depositing an ink composition comprising a nanomaterial anda liquid vehicle having a surface tension less than about 25 dyne/cmfrom an inkjet system including an inkjet cartridge reservoir that feedsink to an ink jet nozzle for printing, the method comprising creating anegative pressure relative to atmospheric pressure inside the inkjetcartridge reservoir which feeds the ink to an ink jet nozzle; andprinting the ink. The method can more consistently inkjet-print inksmade with these solvents with use of an inkjet system including aninkjet cartridge reservoir which feeds the ink to an ink jet nozzle.Creating a negative pressure (relative to atmospheric) inside an inkjetcartridge reservoir can achieve a jet that is more stable. In certainembodiments, this can be accomplished, for example, by placing theinkjet cartridge reservoir below the inkjet nozzle. Preferably, theinkjet cartridge reservoir is held by or positioned relative to theinkjet nozzle(s) such that the height of inkjet cartridge reservoir canbe adjusted to obtain a slight negative pressure inside the cartridgereservoir. The method can facilitate inkjet printing an ink compositioncomprising a nanomaterial and a liquid vehicle having a surface tensionless than about 25 dyne/cm without requiring the addition of surfactantsor other ingredients.

The ability to inkjet print inks having a surface tension less thanabout 25 dyne/cm which include nanomaterials (e.g., semiconductornanocrystals including ligands) without requiring the addition ofseparate surfactants and/or other additives, is advantageous in themanufacture of devices and other electronic structures in which suchadditional additives can have an adverse affect on the chemistry,optical, or electronic properties and/or performance thereof.

In certain embodiments, the ink is deposited onto a surface, including,but not limited to the substrates and other surfaces described herein.

In certain embodiments, the nanomaterial comprises inorganicnanoparticles capable of emitting light.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals. Semiconductor nanocrystals possess characteristics andproperties that make them particularly well-suited for use in a varietyof devices and other end-use applications, including, but not limitedto, light emitting devices, displays, photodetectors, nonvolatile randommemory devices, solar cells, sensors, photovoltaic devices, etc.

In certain embodiments, the nanomaterial comprises semiconductornanocrystals wherein at least a portion of the semiconductornanocrystals include one or more ligands attached to a surface thereof.

In certain embodiments, the method further comprises removal of theliquid vehicle from the ink. In certain embodiments, the liquid vehicleis selected such that, upon removal of the liquid vehicle, the layerincluding the nanomaterial deposited thereon is planar.

In certain embodiments, the liquid vehicle comprises a liquid in whichthe material included in the layer onto which the ink is to be depositedis insoluble.

In accordance with another aspect of the invention there is provided amethod of fabricating a device. The method comprises depositing an inkin accordance with an aspect or embodiment of the invention over asubstrate including an electrode. The substrate may optionally includeone or more additional layers and/or features. In another detailedaspect, following deposition onto the substrate, the liquid vehicle isremoved from the ink. In another detailed aspect, one or more additionallayers and/or features are disposed over the semiconductor nanocrystals.

In accordance with another aspect of the invention, there is provided amethod for forming an array of devices comprising: depositing an ink inaccordance with an aspect or embodiment of the invention in apredetermined arrangement over a substrate including an electrode. Forexample, the ink can be deposited in a patterned or unpatternedarrangement.

The substrate may optionally include one or more additional layersand/or features. In another detailed aspect, following deposition ontothe substrate, the liquid vehicle is removed from the ink. In anotherdetailed aspect, one or more additional layers and/or features aredisposed over the semiconductor nanocrystals. In certain embodiments twoor more inks including different light-emissive materials are depositedin a predetermined arrangement. For example, the ink can be deposited ina patterned or unpatterned arrangement.

In accordance with other aspects of the present invention, there areprovided devices including an ink composition taught herein. In certainembodiments, the ink and/or or composition is included in a component ofthe device. In certain embodiments, the ink and/or composition isincluded on a surface of a component. In certain embodiments, the inkand/or composition can be included as a layer in the device. In certainembodiments, the ink and/or composition is included on a top and/orbottom surface of the device. The ink and/or composition can be includedin a predetermined arrangement over a predetermined region of thesurface on which it is disposed. Such arrangement can be patterned orunpatterned, in accordance with the particular application. In certainembodiments, more than one predetermined arrangement is included. Incertain embodiments, the device comprises a display, a light emittingdevice, or other lighting unit. In certain embodiments, a devicecomprises a photovoltaic device. In certain embodiments, a devicecomprises another electronic or optoelectronic device.

The foregoing, and other aspects described herein all constituteembodiments of the present invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. Other embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 depicts a schematic of an example of an equipment set-up for usein carrying out an embodiment of a method in accordance with theinvention.

FIG. 2 depicts a schematic of an example of a structure of alight-emitting device.

FIG. 3 depicts a schematic of an example of a structure of alight-emitting device.

The attached figures are simplified representations presented forpurposed of illustration only; the actual structures may differ innumerous respects, including, e.g., relative scale, etc.

For a better understanding to the present invention, together with otheradvantages and capabilities thereof, reference is made to the followingdisclosure and appended claims in connection with the above-describeddrawings.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with one aspect of the invention, there is provided an inkcomposition comprising a nanomaterial and a liquid vehicle, wherein theliquid vehicle comprises a perfluorocompound. In certain most preferredembodiments, the liquid vehicle comprises. Fluorinert FC-77, availablefrom 3M.

In certain aspects and embodiments of an ink composition in accordancewith the invention, the ink composition comprises a colloidaldispersion.

In certain embodiments, the liquid vehicle comprises a perfluorocompoundincluding one or more functional groups that are capable of beingcross-linked. In certain embodiments, the functional units can becross-linked by UV treatment. In certain embodiments, the functionalunits can be cross-linked by thermal treatment. In certain embodiments,the functional units can be cross-linked by other cross-linkingtechnique readily ascertainable by a person of ordinary skill in arelevant art. In certain embodiments, the composition including one ormore functional groups that are capable of being cross-linked can be theliquid vehicle itself. In certain embodiments, it can be a co-solvent.In certain embodiments, it can be a component of a mixture with theliquid vehicle.

In accordance with one aspect of the invention, there is provided an inkcomposition comprising a nanomaterial and a liquid vehicle, wherein theliquid vehicle comprises a composition including one or more functionalgroups that are capable of being cross-linked. In certain embodiments,the functional units can be cross-linked by UV treatment. In certainembodiments, the functional units can be cross-linked by thermaltreatment. In certain embodiments, the functional units can becross-linked by other cross-linking technique readily ascertainable by aperson of ordinary skill in a relevant art. In certain embodiments, thecomposition including one or more functional groups that are capable ofbeing cross-linked can be the liquid vehicle itself. In certainembodiments, it can be a co-solvent. In certain embodiments, it can be acomponent of a mixture with the liquid vehicle.

In certain embodiments, the ink can further include scatterers.

In accordance with another aspect of the invention, there is provided anink composition comprising a nanomaterial, a liquid vehicle, andscatterers.

Examples of scatterers (also referred to herein as scattering particles)include, without limitation, metal or metal oxide particles, airbubbles, and glass beads (solid or hollow). Other scatterers can bereadily identified by those of ordinary skill in the art. In certainembodiments, scatterers have a spherical shape. Preferred examples ofscattering particles include, but are not limited to, TiO₂, SiO₂,BaTiO₃, and ZnO. Selection of the size and size distribution of thescatterers is readily determinable by those of ordinary skill in theart. The size and size distribution is preferably based upon therefractive index mismatch of the scattering particle and the hostmaterial in which it the scatterer is to be dispersed after removal ofany liquid medium that may be present, and the preselected wavelength(s)to be scattered according to Rayleigh scattering theory. The surface ofthe scattering particle may further be treated to improve dispersabilityand stability in the host material. In one embodiment, the scatteringparticle comprises TiO₂ (R902+ from DuPont) of 0.2 μm particle size, ina concentration between 0.001% and 20% by weight. In certain preferredembodiments, the concentration range of the scatterers is between 0.1%and 10% by weight. In a certain more preferred embodiments, an inkincludes a scatterer comprising TiO₂ at a concentration in a range fromabout 1% to about 5% by weight.

In certain aspects and embodiments of the invention described herein,the nanomaterial comprises semiconductor nanocrystals.

In certain aspects and embodiments of the invention described herein, anink composition in accordance with an embodiment of the invention canfurther include a variety of components such as those typically used ininkjet liquid vehicles and inks, such as, but not limited to solvents,cosolvents, surfactants, biocides, buffers, viscosity modifiers,sequestering agents, colorants, stabilizing agents, humectants, fillers,extenders, water, and mixtures thereof.

In accordance with another aspect of the invention, there is provided amethod for depositing an ink composition comprising a nanomaterial and aliquid vehicle having a surface tension less than about 25 dyne/cm. Incertain embodiments, the liquid vehicle has a surface tension no greaterthan about 15 dyne/cm. Examples of liquid vehicles having a surfacetension a vehicle less than about 25 dyne/cm include those in whichorganic materials typically used in fabricating various electronicdevices (e.g., light-emitting devices, photodetectors, and other devicesincluding semiconductor nanocrystals) are insoluble. Examples of suchliquid vehicles include fluorinated solvents, such as perfluorodecalin,or the Fluorinert series of solvents sold by 3M. In creating inks fromsuch solvents, the surface tension and viscosity may fall below thosenormally required for inkjet, e.g., 25 dyne/cm. Fluorinert FC-77, forexample, has a surface tension of 13 dyne/cm and a viscosity of 1.3 cP.

In certain embodiments, there is provided a method to more consistentlyinkjet print inks made with these solvents with use of an inkjet systemincluding an inkjet cartridge reservoir which feeds the ink to an inkjet nozzle. The method includes creating a negative pressure (relativeto atmospheric) inside an inkjet cartridge reservoir to form a jet thatis more stable. This can be accomplished, for example, by placing theinkjet cartridge reservoir below the inkjet nozzle. Preferably, theinkjet cartridge reservoir is held by or positioned relative to theinkjet nozzle(s) such that the height of inkjet cartridge reservoir canbe adjusted to obtain a slight negative pressure inside the cartridgereservoir.

In certain embodiments, an ink in accordance with an embodiment of theinvention can be deposited from a micro-dispenser, such as an inkjetprinthead of an inkjet printing system. Inkjet printing can allow apattern of ink including a nanomaterial to be conveniently formed on alayer of a device. Inkjet printing can allow precise control over thelocation and size of inked areas that are printed. Ink spots of about 20μM in size are readily achievable today by commercially available inkjetprinters, and smaller spot sizes are expected to be possible. Differentnanomaterials can be patterned simultaneously using an inkjet printingsystem having multiple print heads. Thus, multiple nanomaterials can bedeposited in a single deposition step. This avoids the need to registersubsequent depositions to a previously deposited pattern.

An inkjet printing system for use in depositing a nanomaterial caninclude a printhead having a firing chamber reservoir containing an ink.In one embodiment, an inkjet printing system, for example, can be usedto propel the ink onto the material or device layer to be printed usingresistive heating elements or piezoelectric elements for propelling thecomposition through an overlying orifice plate. The ink can be stored ina reservoir and the composition can travel through a set ofmicro-channels toward the orifice plate. The printhead can have a firingchamber reservoir containing the ink. Examples of inkjet printingsystems for use in carrying out methods described herein include,without limitation, Dimatix Materials Printer DMP-2800 Series includingDimatix Materials Cartridge DMC-1000 Series, of Dimatix, Inc., SantaClara, Calif. Inkjet printing systems from other manufacturers may alsobe useful in carrying out methods described herein. See also inkjetprinting systems described in U.S. Pat. No. 6,997,539 for “Apparatus forDepositing Droplets” of Hoisington et al. (assigned to Dimatix, Inc.),issued on 14 Feb. 2006; U.S. Pat. No. 7,011,936 for “Piezoelectric InkJet Module With Seal” of Moynihan et al. (assigned to Dimatix, Inc.),issued on 14 Mar. 2006. The foregoing patents are hereby incorporatedherein by reference in their entirety. Examples of other inkjet printingsystems include the Omnidot printer available from the Xaar Corporationheadquartered in Cambridge, UK. Another example of a nozzle array is amulti jet nozzle system that includes 126 jets and is sold under thepart number XJ126 by Xaar Corporation. Furthermore, an atomization sprayprocess using an ultrasonic spray head to dispense ink droplets may beemployed. Additionally, for inks with high viscosities, e.g., 20centipoise or greater, the Leopard available from the Xaar Corporationmay be employed, wherein the ink may be heated to reduce the viscosityto a jettable range.

An example of another inkjet system which is more suitable to researchand development needs is the Active Pipette™ piezo system available fromEngineering Arts.

An inkjet printing system can include, for example, a data interface, acontrol subsystem, a positioning subsystem, and a depositing subsystem.It should be appreciated that in other embodiments of the invention, anink including a nanomaterial comprising semiconductor nanocrystals and aliquid vehicle may be deposited onto a material or device layer by anyof a variety of other delivery systems including one or moremicro-dispensers, including but not limited to thermal ejection,piezoelectric ejection, aerosol generation, micropipettes, pipettes,ultrasonic heads, etc. that can be configured to dispense a selectedvolume of solution with the desired application parameters.

Current inkjet technology allows for orifice sizes of from about 15 μmto about 100 μm. Thus, the minimum size of the features that can bedeposited is currently limited to about this range, although futuredevelopments may allow for smaller orifice sizes and decreased sizes.Additionally, the size of the orifice can affect the practical size ofany nanomaterial present in the ink to be inkjetted.

In certain embodiments, inkjetting techniques can include an inkformulation which is tailored to various inkjet pens, including thermal,piezoelectric, sonic impulse, or other known inkjet printing systems.

As discussed above, an ink composition can further include one or moreof a variety of components such as those typically used in inkjet liquidvehicles and inks, such as, but not limited to solvents, cosolvents,surfactants, biocides, buffers, viscosity modifiers, sequesteringagents, colorants, stabilizing agents, humectants, fillers, extenders,water, and mixtures thereof. Several considerations in selecting theamount of liquid vehicle include those related to nucleation such asheat capacity, heat of vaporization, critical nucleation temperature,diffusivity, and the like. Typically, an ink for use in thermal inkjetprinting systems can have a viscosity of from about 0.8 cP to about 20cP, and in some cases, can be up to 50 cP. Similarly, an ink for use inpiezoelectric inkjet printing systems can have a viscosity of from about2 cP to about 15 cP, and in some cases, can be up to 30 cP. Optionally,a viscosity modifier can be included in the ink. Examples of viscositymodifiers include 2-pyrrolidone, isopropyl alcohol, glycerol, and thelike. However, other viscosity modifiers can be used.

In certain embodiments, an ink in accordance with an embodiment of theinvention can be deposited from a micro-dispenser, such as an inkjetprinthead of an inkjet printing system. Inkjet printing can allow apattern of ink including a nanomaterial to be conveniently formed on alayer of a device. Inkjet printing can allow precise control over thelocation and size of inked areas that are printed. Ink spots of about 20μm in size are readily achievable today by commercially available inkjetprinters, and smaller spot sizes are expected to be possible. Differentnanomaterials can be patterned simultaneously using an inkjet printingsystem having multiple print heads. Thus, multiple nanomaterials can bedeposited in a single deposition step. This avoids the need to registersubsequent depositions to a previously deposited pattern.

The surface tension of an ink used in thermal inkjet printing systemscan range from about 25 dyne/cm to about 75 dyne/cm, and in someembodiments, can be from about 30 to about 55 dyne/cm. The surfacetension can be adjusted using compounds such as isopropyl alcohol,ethanol, methanol, glycerol, and the like. In certain embodiments, theliquid vehicle can include from about 60 wt % to about ˜100 wt % of theink. Various techniques can be used to modify the viscosity or otherjetting properties of the ink. For example, heat can be used to liquefymaterial, increase solubility of the material, or reduce viscosity suchthat it becomes inkjettable. Those skilled in the art will recognizethat the above discussion is primarily focused on thermal inkjetprinting systems; piezoelectric inkjet printing systems involve lessrestrictive considerations. For example, thermal inkjet printing systemsare typically operated at temperatures below about 80° C., whilepiezoelectric inkjet printing systems can be operated at temperatures ofup to about 150° C. Those skilled in the art will recognize whichcomponents can be included in the liquid vehicle in order to inkjet anink from thermal, piezoelectric, or other inkjet printing systems. Thoseskilled in the art can adjust these and other variables to achieve avariety of resolutions and conductive paths. Printhead waveforms (e.g.,piezo and thermal excitation waveforms, anti-clogging waveforms,ejection waveforms, etc.), and the compositions of the materials used toconstruct the printhead and orifice plate are among such variables. Forexample, depending on the wetting attributes of the ink and thewettability of the internal surface of the inkjet nozzle or the surfaceof the printing orifice plate, the ink composition can be treated toenhance drop ejection.

In certain embodiments of the inventions described herein, it may bebeneficial to use a vehicle system which would result in ink propertiesfalling outside the normal ranges described above. This would be thecase, for example, if one were to use a vehicle in which the material ofthe device is insoluble. An example of a class of solvents that meetthis criterion are fluorinated solvents, such as perfluorodecalin, orthe Fluorinert series of solvents sold by 3M. In creating inks from suchsolvents, the surface tension and viscosity may fall below thosenormally required for inkjet. Fluorinert FC-77, for example, has asurface tension of 13 dyne/cm and a viscosity of 1.3 cP. A method tomore consistently jet inks made with these solvents includes creating anegative pressure (relative to atmospheric) inside the cartridgereservoir to form a jet that is more stable. This can be accomplished atlaboratory scale by placing the cartridge reservoir slightly below theinkjet nozzle. The positioning of the cartridge reservoir to achieve asufficient negative pressure therein to form a jet can be readilydetermined by one of ordinary skill in the art. Preferably, the inkjetcartridge reservoir is held by or positioned relative to the inkjetnozzle(s) such that the height of inkjet cartridge reservoir can beadjusted to obtain the desired negative pressure inside the cartridgereservoir. In one example, the cartridge reservoir is positioned on avariable-height platform (e.g., a small jack), the height of which canbe adjusted to obtain a negative pressure inside the cartridgereservoir, preferably a slight negative pressure. A schematic diagram ofan example of a laboratory-scale set-up is shown in FIG. 1. In certainembodiments, semiconductor nanocrystals included in a fluorinatedsolvent include one or more fluorinated ligands attached to a surface ofthe nanocrystals. Nanocrystals including fluorinated ligands can beprepared by exchanging at least one or more ligands that become attachedto a nanocrystal surface during, e.g., colloidal synthesis, with ligandsthat include a functional head such as, by way of example, a thiol,carbodithioate, carbodithioic acid, amine, thiourea, amide, phosphineoxide, phosphonic or phosphinic acid, thiophosphonic or thiophosphinicacid, which functional head can be substituted with alkyl and/or arylunits that are perfluorinated or partially fluorinated. Preferably thefluorinated ligand is chemically compatible with the fluorinated liquidvehicle.

Deposition of nanomaterial onto the surface to be printed in the form ofejected drops produces a “dot” of ink comprising a nanomaterial andliquid vehicle thereon. The term “dot” is used to refer to the ink droponce it contacts the surface. In some examples, the ink in the drop willstay in a thin layer on the surface. However, depending on the porosity,wettability, and/or or other attributes of the device layer, and whenthe drop contacts the layer, the ink can spread outwardly resulting indot gain. Dot gain is the ratio of the final diameter of a dot on thesurface to its initial diameter. If the material or layer onto which theink is deposited is porous, the dot can penetrate into the material orlayer. Dot penetration is the depth that the drop soaks into the surfaceon which it is deposited. The physical and/or chemical properties of thedots can enhance dissolution rates without disrupting the permeabilityand specificity of the ink. Controlled dot placement, highsurface-to-mass ratio of the dots, and digital mass deposition controlof the dots can be used to address performance of the depositednanomaterial in the device.

For example, a dot has virtually no dot gain or dot penetration, as maybe the case, when an ejection solution is applied to a deliverysubstrate having a nonwettable, surface, or a relatively impermeablesurface.

One convenient way of quantifying the nature of the interaction betweenthe ink forming the dot and the surface onto which it is deposited, isto measure the angle θ formed by the liquid-solid and the liquid-airinterfaces. This angle, referred to as the contact angle, is a productof the surface tension of the solution as well as the wettability of thesurface onto which the ink is deposited. Inks including a liquid vehiclehaving a high surface tension, and poor interaction with the surface ofthe device layer to be printed tend to exhibit contact angles greaterthan 90°. The ink then tends to form discrete droplets on the surface.However, where the liquid vehicle is relatively nonpolar, as istypically the case with an organic liquid, and the surface onto whichthe ink is deposited device layer is similarly nonpolar, the contactangle is typically less than 90°, and the liquid tends to spread out andform a thin film. As the dot spreads out and thins, the contact angletends to zero.

As described above, an inkjet printing system may be adapted to depositone or more different nanomaterials comprising different semiconductornanocrystals, which may be included in corresponding inks. In someembodiments, two or more ejection cartridges can be configured for eachto deposit an ink including a different nanomaterial and/or eject inkhaving different drop volumes. The inkjet system may be configured tointerchangeably receive different ejection cartridges, which areindividually configured to apply the same of different ink to thesurface being printed. Interchangeable ejection cartridges may also beused to replace an empty ejection cartridge with a full ejectioncartridge. It is within the scope of this disclosure to utilize othermechanisms for depositing an ink including a nanomaterial and a liquidvehicle onto a material or layer of a device, and ejection cartridge isprovided as a nonlimiting example. For example, an inkjet system mayinclude an ejection cartridge that utilizes an ejection-head havingejectors configured to effectuate fluid ejection via a nonthermalmechanism, such as vibrational displacement caused by a piezoelectricejection element.

In one example of an inkjet system that may be useful in carrying outmethods in accordance with the invention, the nozzle spacing can beabout 504 μm; the nozzle diameter can be about 27 μm; and the dropletsize (for 12 pl) spreads to minimum size ˜5 μm square.

Based on estimated nozzle life, a nozzle can be expected to coat an areaof about 807 ft2. This area corresponds to printing 29,000 two-inchsquares or 3,200 six inch square displays. The range of fluidviscosities that can be inkjet printed includes, for example, 8-14 cP.Printing at operating temperatures over 70° C. may be limited by thespecific materials and equipment used.

Depending upon the drop volume, contact angle, viscosity, and otherproperties of the ink, even with a drop volume as small as ˜8 pl, thespot diameter can be relatively large due to rapid spreading. Similarly,depending upon the drop volume, contact angle, viscosity, and otherproperties of the ink, in some instances, to print a linear pattern froman inkjet printing system, repeat printing of drops in an overlappingarrangement may be appropriate.

An ink in accordance with an embodiment of the present invention can beuseful for depositing nanomaterial from a micro-dispenser. In certainembodiments, the liquid vehicle comprises a liquid in which thenanomaterial can be dispersed or suspended. In certain preferredembodiments, the nanomaterial is colloidally dispersed. In certainembodiments, the liquid vehicle comprises a liquid in which thenanomaterial does not dissolve or does not appreciably dissolve (e.g.,solubility is less than 0.001 mg/ml).

In certain embodiments including a nanomaterial with one or more ligandsattached to a surface of at least a portion of the nanoparticlesthereof, the liquid vehicle comprises a liquid in which suchnanomaterial with attached ligands can be dispersed or suspended. Incertain preferred embodiments, the nanomaterial is colloidallydispersed. In certain embodiments, the nanoparticles comprisesemiconductor nanocrystals. In certain embodiments, the liquid vehicleis one in which the ligands (when not attached to nanoparticles) are atleast partially soluble. In certain embodiments, the liquid vehicle isone in which the ligands (when not attached to nanoparticles) areinsoluble.

In certain embodiments, the ink includes a liquid vehicle in which thematerial or device layer onto which the ink is to be deposited isinsoluble (e.g., <0.001/mg/ml of the material dissolves in the liquidvehicle). In other certain embodiments, the ink includes a liquidvehicle in which the material or device layer onto which the ink is tobe deposited is at least partially soluble (e.g., >0.001 mg/ml of thematerial dissolves in the liquid vehicle). In certain embodiments, atleast a portion of the nanomaterial can become at least temporarilymixed in the portion of the material or layer that dissolves in the ink.

In certain embodiments, the method further comprises removal of theliquid vehicle from the ink.

In certain embodiments, the liquid vehicle can be removed such that atleast a portion of the material or layer and the nanomaterial remainmixed.

In another embodiment, the liquid vehicle can be removed such that thenanomaterial phase separates to form a layer of nanomaterial at or nearthe surface of the underlying material or layer. Phase separation isdescribed in more detail in U.S. patent application Ser. No. 10/400,907for “Layered Materials Including Nanoparticles” of Bulovic et al. filedon 28 Mar. 2003, which is hereby incorporated herein by reference in itsentirety.

In certain embodiments, the liquid vehicle of the ink is selected suchthat, upon removal of the liquid vehicle, the material or layer(s) ofthe device including the nanomaterial deposited thereon is planar. Anexample of a technique for achieving a planar material or device layerinvolves utilizing a well structure such as typically used in PLEDtechnology. Other techniques can be readily determined by one ofordinary skill in the relevant art. One technique for measuringplanarity is by measuring peak-to-peak height difference. This can bereadily measured using an AFM microscope. In certain embodiments, aplanar layer has a peak-to-peak height difference less than about 5%.

Examples of a liquid vehicle for inclusion in an ink including ananomaterial (e.g., a nanomaterial comprising semiconductornanocrystals) include, without limitation, those listed in the followingTable 1, and mixtures of two or more thereof.

Examples of mixtures include, but are not limited to, hexane and octane;benzene and xylene; tetrahydrofurane and anisole; etc.

TABLE 1 Relative Boiling Polarity Viscosity Point (compared LiquidFormula @25° C. @1 atm to water) cyclohexane C₆H₁₂ 0.89 80.7 0.006pentane C₅H₁₂ 0.24 36.1 0.009 Hexane C₆H₁₄ 0.30 69 0.009 heptane C₇H₁₆0.91 98 0.012 Carbon tetrachloride CCl₄ 0.91 76.7 0.052 p-xylene C₈H₁₀0.63 138.3 0.074 toluene C₇H₈ 0.56 110.6 0.099 Benzene C₆H₆ 0.60 80.10.111 Diethyl ether C₄H₁₀O 0.22 34.6 0.117 Methyl t-butyl C₅H₁₂O 55.20.148 alcohol Dioxane C₄H₈O₂ 1.21 101.1 0.164 tetrahydrofurane C₄H₈O0.47 66 0.207 (THF) ethyl acetate C₄H₈O₂ 77 0.228 dimethoxy-ethaneC₄H₁₀O₂ 85 0.231 (glyme) Diglyme C₆H₁₄O₃ 162 0.244 chloroform CHCl₃ 0.5461.2 0.259 methylene chloride CH₂Cl₂ 0.43 39.8 0.309 2-butanone C₄H₈O79.6 0.327 Acetone C₃H₆O 0.31 56.2 0.355 t-butyl alcohol C₄H₁₀O 82.20.389 dimethyl-formamide C₃H₇NO 153 0.404 (DMF) dimethyl sulfoxideC₂H₆OS 189 0.444 (DMSO) Acetonitrile C₂H₃N 0.35 81.6 0.46 2-propanolC₃H₈O 2.40 82.4 0.546 1-butanol C₄H₁₀O 3.00 117.6 0.602 1-propanol C₃H₈O1.95 97 0.617 acetic acid C₂H₄O₂ 118 0.648 ethanol C₂H₆O 1.20 78.5 0.654diethylene glycol C₄H₁₀O₃ 35.70 245 0.713 Methanol CH₄O 0.59 64.6 0.762ethylene glycol C₂H₆O₂ 16.90 197 0.79 Glycerin C₃H₈O₃ 1410.00 290 0.812water, heavy (D2O) D₂O 101.3 0.991 Water H₂O 1.00 100 1 Nonane(CH₃(CH₂)₇CH₃) 0.67 39.0 Decane C₁₀H₂₂ 0.84 174.1 Dodecane C₁₂H₂₆ 1.25216.2 Chlorobenzene C₆H₅Cl 0.75 132 Dichlorobenzene C₆H₄Cl₂ — 174.0Anisole C₇H₈O 0.92 154.0 Dimethyl HCON(CH₃)₂ 0.79 149.56 formamide1-Methyl-2- 1.7 204.5 pyrrolidinone Carbon tetrachloride CCl₄ 0.91 76.81,1,1-Trichloro- CH₃CCl₃ 0.73 74.0 ethane Tetrachloroethylene ClCH═CCl₂0.57 87.0 Ethylbenzene C₈H₁₀ 0.67 136.0 Fluorinert FC-77 1.3 97.0 (a 3Mproduct)

Other liquids or mixtures of liquids can be used as a liquid vehicle. Incertain embodiments, volatile liquids or mixtures of volatile liquidscan be used as a liquid vehicle.

In certain embodiments, an ink including a nanomaterial and a liquidvehicle has a viscosity in a range of from about 0.1 centipoise (e.g.,that of diethyl ether, methanol) to greater than 1500 centipoise (e.g.,that of oils, glycerol).

In certain embodiments including a nanomaterial comprising semiconductornanocrystals, the liquid vehicle comprises an organic non-polar liquid.In certain embodiments, the liquid vehicle has a viscosity less than orequal to about 1 cP and also relatively high volatility.

In certain aspects and embodiments of the inventions described herein,it is not necessary to have the nanomaterial particles (e.g.,semiconductor nanocrystals) individually dispersed in the vehicle. Thenanomaterial particles (e.g., semiconductor nanocrystals may beaggregated. In certain aspects and embodiments of the inventionsdescribed herein, the nanomaterial particles (e.g., semiconductornanocrystals) may be included within or adsorbed onto polymer particles.In certain embodiments of the inventions described herein, thenanomaterial particles (e.g., semiconductor nanocrystals) may beincluded within or adsorbed onto a matrix. The matrix can be polymericor non-polymeric.

In certain aspects and embodiments of the invention described herein, anink composition in accordance with an embodiment of the invention canfurther comprises a material capable of transporting charge. In certainembodiments, the material capable of transporting charge has a tripletenergy which is at least greater than the bandgap of the semiconductornanocrystals included in the ink. In certain embodiments, the materialcapable of transporting charge included in the ink composition is atleast partially soluble in the liquid vehicle.

Optionally, other components can be included in the ink. Examples ofother components that can be optionally included in the ink include, butare not limited to, e.g., surfactants, solvents, co-solvents, buffers,biocides, viscosity modifiers, complexing agents, chelating agents,stabilizing agents (e.g., to inhibit agglomeration of the nanomaterial),humectants, fillers, extenders etc. Other possible components includeother additives of the type that may be included in ink or inkjet inkcompositions. Stabilizing agents can include, e.g., chemically attachedfunctional groups or ligands to form a coating around individualnanoparticles.

The amount (e.g., concentration (wt/vol)) of nanomaterial included in anink can be selected based upon the particular nanomaterial and desiredattributes of the deposited nanomaterial (e.g., thickness, opticaldensity, features of the deposited nanomaterial (e.g., patterned orunpatterned, sizes of the features of a pattern, etc.)). The amount canbe readily determined by a person of ordinary skill in the art.

For example, in certain embodiments of inks including a nanomaterialcomprising semiconductor nanocrystals and a liquid vehicle (including,e.g., but not limited to, a liquid vehicle comprising non-polar organicliquid or liquid mixture), the ink can include at least about 0.1 mg/mlsemiconductor nanocrystals. In examples of other embodiments, the inkcan include at least 1 mg/ml, at least 5 mg/ml, at least 10 mg/ml, atleast 25 mg/ml; at least 50 mg/ml, etc.

In certain embodiments, the nanomaterial and any other optionalcomponents are dispersed in the ink when deposited. In certain preferredembodiments, the dispersion is colloidal.

A nanomaterial includes nanoparticles having an average maximumdimension smaller than 100 nm.

In certain preferred embodiments, the nanomaterial comprisessemiconductor nanocrystals.

Semiconductor nanocrystals comprise nanometer-scale inorganicsemiconductor particles. Semiconductor nanocrystals preferably have anaverage nanocrystal diameter less than about 150 Angstroms (Å), and mostpreferably in the range of 12-150 Å.

Semiconductor nanocrystals include, for example, inorganic crystallitesbetween about 1 nm and about 1000 nm in diameter, preferably betweenabout 2 nm and about 50 nm, more preferably about 5 nm to about 20 nm(such as about 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20nm).

The semiconductor forming the semiconductor nanocrystals can comprise aGroup IV element, a Group II-VI compound, a Group II-V compound, a GroupIII-VI compound, a Group III-V compound, a Group IV-VI compound, a GroupI-III-VI compound, a Group II-IV-VI compound, a Group II-IV-V compound,alloys of any of the foregoing, and/or mixtures of any of the foregoing,including ternary and quaternary mixtures and/or alloys. Examplesinclude, but are not limited to, ZnO, ZnS, ZnSe, ZnTe, MgO, MgS, MgSe,MgTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb,GaN, GaP, GaAs, GaSb, GaSe, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb,PbO, PbS, PbSe, PbTe, Si, Ge, other Group IV elements, and/or mixturesor alloys thereof, including ternary and quaternary mixtures or alloys.

Examples of the shape of semiconductor nanocrystals include sphere, rod,disk, other shape or mixtures thereof.

Preferably, the semiconductor nanocrystals include a “core” of one ormore first semiconductor materials, which may be surrounded by anovercoating or “shell” of one or more second semiconductor materials. Asemiconductor nanocrystal core surrounded by a semiconductor shell isalso referred to as a “core/shell” semiconductor nanocrystal.

For example, the semiconductor nanocrystal can include a core having theformula MX, where M is cadmium, zinc, magnesium, mercury, aluminum,gallium, indium, thallium, or mixtures thereof, and X is oxygen, sulfur,selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, ormixtures thereof. Examples of materials suitable for use assemiconductor nanocrystal cores include, but are not limited to, CdO,CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, MgO, MgS, MgSe, MgTe, GaAs, GaP,GaSb, GaN, HgO, HgS, HgSe, HgTe, InAs, InP, InSb, InN, AlAs, AlP, AlSb,AIS, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, Ge, Si, other Group IVelements, and/or mixtures or alloys thereof, including ternary andquaternary mixtures or alloys.

The shell can be a semiconductor material having a composition that isthe same as or different from the composition of the core. The shellcomprises an overcoat of a semiconductor material on a surface of thecore semiconductor nanocrystal can include a Group IV element, a GroupII-VI compound, a Group II-V compound, a Group III-VI compound, a GroupIII-V compound, a Group IV-VI compound, a Group I-III-VI compound, aGroup II-IV-VI compound, a Group II-IV-V compound, alloys of any of theforegoing, and/or mixtures of any of the foregoing, including ternaryand quaternary mixtures and/or alloys. Examples include, but are notlimited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgO, MgS, MgSe,MgTe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP,InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe,Si, Ge, other Group IV elements, and/or mixtures and/or alloys thereof,including ternary and quaternary mixtures and/or alloys. For example,ZnS, ZnSe or CdS overcoatings can be grown on CdSe or CdTe semiconductornanocrystals. An overcoating process is described, for example, in U.S.Pat. No. 6,322,901. By adjusting the temperature of the reaction mixtureduring overcoating and monitoring the absorption spectrum of the core,over coated materials having high emission quantum efficiencies andnarrow size distributions can be obtained. The overcoating may compriseone or more layers. The overcoating comprises at least one semiconductormaterial which is the same as or different from the composition of thecore. Preferably, the overcoating has a thickness of from about one toabout ten monolayers. An overcoating can also have a thickness greaterthan ten monolayers. In certain embodiments, more than one overcoatingcan be included on a core.

In certain embodiments, the surrounding “shell” material can have a bandgap greater than the band gap of the core material. In certainembodiments, the surrounding shell material can have a band gap lessthan the band gap of the core material.

In certain embodiments, the shell can be chosen so as to have an atomicspacing close to that of the “core” substrate. In certain embodiments,the shell and core materials can have the same crystal structure.

Examples of semiconductor nanocrystal (core)shell materials include,without limitation: red (e.g., (CdSe)ZnS (core)shell), green (e.g.,(CdZnSe)CdZnS (core)shell, etc.), and blue (e.g., (CdS)CdZnS(core)shell.

Additional examples of core/shell semiconductor structures are describedin U.S. application Ser. No. 10/638,546, for “Semiconductor NanocrystalHeterostructures”, filed 12 Aug. 2003, and U.S. Published PatentApplication No. US 2004-0023010 A1, for “Light Emitting Device IncludingSemiconductor Nanocrystals” of Bulovic et al. The foregoing applicationsare hereby incorporated herein by reference in its entirety.

Preparation and manipulation of semiconductor nanocrystals aredescribed, for example, in U.S. Pat. Nos. 6,322,901 and 6,576,291, andU.S. Patent Application No. 60/550,314, each of which is herebyincorporated herein by reference in its entirety. One method ofmanufacturing a semiconductor nanocrystal is a colloidal growth process.Colloidal growth occurs by injection an M donor and an X donor into ahot coordinating solvent. One example of a preferred method forpreparing monodisperse semiconductor nanocrystals comprises pyrolysis oforganometallic reagents, such as dimethyl cadmium, injected into a hot,coordinating solvent. This permits discrete nucleation and results inthe controlled growth of macroscopic quantities of semiconductornanocrystals. The injection produces a nucleus that can be grown in acontrolled manner to form a semiconductor nanocrystal. The reactionmixture can be gently heated to grow and anneal the semiconductornanocrystal. Both the average size and the size distribution of thesemiconductor nanocrystals in a sample are dependent on the growthtemperature. The growth temperature necessary to maintain steady growthincreases with increasing average crystal size. The semiconductornanocrystal is a member of a population of semiconductor nanocrystals.As a result of the discrete nucleation and controlled growth, thepopulation of semiconductor nanocrystals that can be obtained has anarrow, monodisperse distribution of diameters. The monodispersedistribution of diameters can also be referred to as a size. Preferably,a monodisperse population of particles includes a population ofparticles wherein at least 60% of the particles in the population fallwithin a specified particle size range. A population of monodisperseparticles preferably deviate less than 15% rms (root-mean-square) indiameter and more preferably less than 10% rms and most preferably lessthan 5%.

In certain embodiments, the preparation of semiconductor nanocrystalscan be carried out in the presence of an amine. See, for example, U.S.Pat. No. 6,576,291 for “Preparation of Nanocrystallites” of Bawendi etal. issued 10 Jun. 2003, which is hereby incorporated herein byreference in its entirety.

The narrow size distribution of the semiconductor nanocrystals allowsthe possibility of light emission in narrow spectral widths.Monodisperse semiconductor nanocrystals have been described in detail inMurray et al. (J. Am. Chem. Soc., 115:8706 (1993)); in the thesis ofChristopher Murray, “Synthesis and Characterization of II-VI QuantumDots and Their Assembly into 3-D Quantum Dot Superlattices”,Massachusetts Institute of Technology, September, 1995; and in U.S.patent application Ser. No. 08/969,302 for “Highly LuminescentColor-Selective Materials”. The foregoing are hereby incorporated hereinby reference in their entireties.

The process of controlled growth and annealing of the semiconductornanocrystals in the coordinating solvent that follows nucleation canalso result in uniform surface derivatization and regular corestructures. As the size distribution sharpens, the temperature can beraised to maintain steady growth. By adding more M donor or X donor, thegrowth period can be shortened. The M donor can be an inorganiccompound, an organometallic compound, or elemental metal. M is cadmium,zinc, magnesium, mercury, aluminum, gallium, indium or thallium. The Xdonor is a compound capable of reacting with the M donor to form amaterial with the general formula MX. The X donor can be a chalcogenidedonor or a pnictide donor, such as a phosphine chalcogenide, abis(silyl) chalcogenide, dioxygen, an ammonium salt, or a tris(silyl)pnictide. Suitable X donors include dioxygen, bis(trimethylsilyl)selenide ((TMS)₂Se), trialkyl phosphine selenides such as(tri-noctylphosphine) selenide (TOPSe) or (tri-n-butylphosphine)selenide (TBPSe), trialkyl phosphine tellurides such as(tri-n-octylphosphine) telluride (TOPTe) or hexapropylphosphorustriamidetelluride (HPPTTe), bis(trimethylsilyl)telluride ((TMS)₂Te),bis(trimethylsilyl)sulfide ((TMS)₂S), a trialkyl phosphine sulfide suchas (tri-noctylphosphine) sulfide (TOPS), an ammonium salt such as anammonium halide (e.g., NH4Cl), tris(trimethylsilyl)phosphide ((TMS)₃P),tris(trimethylsilyl) arsenide ((TMS)₃As), or tris(trimethylsilyl)antimonide ((TMS)₃Sb). In certain embodiments, the M donor and the Xdonor can be moieties within the same molecule.

A coordinating solvent can help control the growth of the semiconductornanocrystal. The coordinating solvent is a compound having a donor lonepair that, for example, has a lone electron pair available to coordinateto a surface of the growing semiconductor nanocrystal. Solventcoordination can stabilize the growing semiconductor nanocrystal.Examples of coordinating solvents include alkyl phosphines, alkylphosphine oxides, alkyl phosphonic acids, or alkyl phosphinic acids,however, other coordinating solvents, such as pyridines, furans, andamines may also be suitable for the semiconductor nanocrystalproduction. Examples of suitable coordinating solvents include pyridine,tri-n-octyl phosphine (TOP), tri-n-octyl phosphine oxide (TOPO) andtrishydroxylpropylphosphine (tHPP). Technical grade TOPO can be used.Non-coordinating solvents can also be used.

Size distribution during the growth stage of the reaction can beestimated by monitoring the absorption or emission line widths of theparticles. Modification of the reaction temperature in response tochanges in the absorption spectrum of the particles allows themaintenance of a sharp particle size distribution during growth.Reactants can be added to the nucleation solution during crystal growthto grow larger crystals. For example, for CdSe and CdTe, by stoppinggrowth at a particular semiconductor nanocrystal average diameter andchoosing the proper composition of the semiconducting material, theemission spectra of the semiconductor nanocrystals can be tunedcontinuously over the wavelength range of 300 nm to 5 microns, or from400 nm to 800 nm.

The particle size distribution of the semiconductor nanocrystals can befurther refined by size selective precipitation with a poor solvent forthe semiconductor nanocrystals, such as methanol/butanol as described inU.S. Pat. No. 6,322,901. For example, semiconductor nanocrystals can bedispersed in a solution of 10% butanol in hexane. Methanol can be addeddropwise to this stirring solution until opalescence persists.Separation of supernatant and flocculate by centrifugation produces aprecipitate enriched with the largest crystallites in the sample. Thisprocedure can be repeated until no further sharpening of the opticalabsorption spectrum is noted. Size-selective precipitation can becarried out in a variety of solvent/nonsolvent pairs, includingpyridine/hexane and chloroform/methanol. The size-selected semiconductornanocrystal population preferably has no more than a 15% rms deviationfrom mean diameter, more preferably 10% rms deviation or less, and mostpreferably 5% rms deviation or less.

As discussed herein, in certain embodiments, the nanomaterial comprisessemiconductor nanocrystals wherein at least a portion of thesemiconductor nanocrystals include one or more ligands attached to asurface thereof.

In one embodiment, the ligands are derived from the coordinating solventused during the growth process. The surface can be modified by repeatedexposure to an excess of a competing coordinating group to form anoverlayer. For example, a dispersion of the capped semiconductornanocrystal can be treated with a coordinating organic compound, such aspyridine, to produce crystallites which disperse readily in pyridine,methanol, and aromatics but no longer disperse in aliphatic solvents.Such a surface exchange process can be carried out with any compoundcapable of coordinating to or bonding with the outer surface of thesemiconductor nanocrystal, including, for example, phosphines, thiols,amines and phosphates. The semiconductor nanocrystal can be exposed toshort chain polymers which exhibit an affinity for the surface and whichterminate in a moiety having an affinity for a liquid medium in whichthe semiconductor nanocrystal is suspended or dispersed. Such affinityimproves the stability of the suspension and discourages flocculation ofthe semiconductor nanocrystal.

The organic ligands can be useful in facilitating large area,non-epitaxial deposition of highly stable inorganic nanocrystals withina device.

More specifically, the coordinating ligand can have the formula:

(Y—)_(k-n)—(X)-(−L)_(n)

wherein k is 2, 3 or 5, and n is 1, 2, 3, 4 or 5 such that k-n is notless than zero; X is O, S, S═O, SO2, Se, Se═O, N, N═O, P, P═O, As, orAs═O; each of Y and L, independently, is aryl, heteroaryl, or a straightor branched C2-12 hydrocarbon chain optionally containing at least onedouble bond, at least one triple bond, or at least one double bond andone triple bond. The hydrocarbon chain can be optionally substitutedwith one or more C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy,hydroxyl, halo, amino, nitro, cyano, C3-5 cycloalkyl, 3-5 memberedheterocycloalkyl, aryl, heteroaryl, C1-4 alkylcarbonyloxy, C1-4alkyloxycarbonyl, C1-4 alkylcarbonyl, or formyl. The hydrocarbon chaincan also be optionally interrupted by —O—, —S—, —N(R_(a))—,—N(R_(a))—C(O)—O—, —O—C(O)—N(R_(a))—, —N(R_(a))—C(O)—N(R_(b))—,—O—C(O)—O—, —P(R_(a))—, or —P(O)(R_(a))—. Each of R_(a) and R_(b),independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxy,hydroxylalkyl, hydroxyl, or haloalkyl. An aryl group is a substituted orunsubstituted cyclic aromatic group. Examples include phenyl, benzyl,naphthyl, tolyl, anthracyl, nitrophenyl, or halophenyl. A heteroarylgroup is an aryl group with one or more heteroatoms in the ring, forinstance furyl, pyridyl, pyrrolyl, phenanthryl.

A suitable coordinating ligand can be purchased commercially or preparedby ordinary synthetic organic techniques, for example, as described inJ. March, Advanced Organic Chemistry, which is hereby incorporated byreference in its entirety.

Other ligands are described in U.S. patent application Ser. No.10/641,292 for “Stabilized Semiconductor Nanocrystals”, filed 15 Aug.2003, which is hereby incorporated herein by reference in its entirety.

When the electron and hole localize on a semiconductor nanocrystal,emission can occur at an emission wavelength. The emission has afrequency that corresponds to the band gap of the quantum confinedsemiconductor material. The band gap is a function of the size of thesemiconductor nanocrystal. Semiconductor nanocrystals having smalldiameters can have properties intermediate between molecular and bulkforms of matter. For example, semiconductor nanocrystals based onsemiconductor materials having small diameters can exhibit quantumconfinement of both the electron and hole in all three dimensions, whichleads to an increase in the effective band gap of the material withdecreasing crystallite size. Consequently, both the optical absorptionand emission of semiconductor nanocrystals shift to the blue, or tohigher energies, as the size of the crystallites decreases.

The emission from a semiconductor nanocrystal can be a narrow Gaussianemission band that can be tuned through the complete wavelength range ofthe ultraviolet, visible, or infra-red regions of the spectrum byvarying the size of the semiconductor nanocrystal, the composition ofthe semiconductor nanocrystal, or both. For example, CdSe can be tunedin the visible region and InAs can be tuned in the infra-red region. Thenarrow size distribution of a population of semiconductor nanocrystalscan result in emission of light in a narrow spectral range. Thepopulation can be monodisperse preferably exhibits less than a 15% rms(root-mean-square) deviation in diameter of the semiconductornanocrystals, more preferably less than 10%, most preferably less than5%. Spectral emissions in a narrow range of no greater than about 75 nm,preferably 60 nm, more preferably 40 nm, and most preferably 30 nm fullwidth at half max (FWHM) for semiconductor nanocrystals that emit in thevisible can be observed. IR-emitting semiconductor nanocrystals can havea FWHM of no greater than 150 nm, or no greater than 100 nm. Expressedin terms of the energy of the emission, the emission can have a FWHM ofno greater than 0.05 eV, or no greater than 0.03 eV. The breadth of theemission decreases as the dispersity of semiconductor nanocrystaldiameters decreases. Semiconductor nanocrystals can have high emissionquantum efficiencies such as greater than 10%, 20%, 30%, 40%, 50%, 60%,70%, or 80%.

The narrow FWHM of semiconductor nanocrystals can result in saturatedcolor emission. This can lead to efficient lighting devices even in thered and blue parts of the visible spectrum, since in semiconductornanocrystal emitting devices no photons are lost to infra-red and UVemission. The broadly tunable, saturated color emission over the entirevisible spectrum of a single material system is unmatched by any classof organic chromophores (see, for example, Dabbousi et al., J. Phys.Chem. 101, 9463 (1997), which is incorporated by reference in itsentirety). A monodisperse population of semiconductor nanocrystals willemit light spanning a narrow range of wavelengths. A device includingsemiconductor nanocrystals of different compositions, sizes, and/orstructures can emit light in more than one narrow range of wavelengths.The color of emitted light perceived by a viewer can be controlled byselecting appropriate combinations of semiconductor nanocrystal sizesand materials in the device as well as relative subpixel currents. Thedegeneracy of the band edge energy levels of semiconductor nanocrystalsfacilitates capture and radiative recombination of all possibleexcitons, whether generated by direct charge injection or energytransfer. The maximum theoretical semiconductor nanocrystal lightingdevice efficiencies are therefore comparable to the unity efficiency ofphosphorescent organic light-emitting devices. The excited statelifetime (τ) of the semiconductor nanocrystal is much shorter (τ˜10 ns)than a typical phosphor (τ>0.1 μs), enabling semiconductor nanocrystallighting devices to operate efficiently even at high current density andhigh brightness.

Transmission electron microscopy (TEM) can provide information about thesize, shape, and distribution of the semiconductor nanocrystalpopulation. Powder X-ray diffraction (XRD) patterns can provide the mostcomplete information regarding the type and quality of the crystalstructure of the semiconductor nanocrystals. Estimates of size are alsopossible since particle diameter is inversely related, via the X-raycoherence length, to the peak width. For example, the diameter of thesemiconductor nanocrystal can be measured directly by transmissionelectron microscopy or estimated from X-ray diffraction data using, forexample, the Scherrer equation. It also can be estimated from the UV/Visabsorption spectrum.

Ink compositions in accordance with the invention can be deposited ontoa surface.

Examples of typical surfaces include a material or device layer or othersubstrate.

In certain embodiments, the substrate can be, for example, a web, afilm, a tape, a flexible sheet, etc. Such forms of substrates cancomprise, for example, plastic, foil, paper, etc. In certainembodiments, a substrate can comprise a sheet of material, a roll ofmaterial, etc. The dimensions of a substrate can vary as a function ofthe intended use thereof. In certain embodiments, a non-rigid substrateis desirable. In certain embodiments, a flexible substrate is preferred.

In certain embodiments, the substrate can be a top or bottom surface ofa light emitting device or other lighting unit.

In certain embodiments, a substrate can further include a layer of adevice disposed over a substrate. In these embodiments, the layer of adevice comprises a material and the ink is deposited onto the layer.

In certain embodiments, the ink is deposited onto a layer of a devicedisposed over a substrate. In certain embodiments, the substrate furtherincludes a layer of a device disposed over the substrate. In theseembodiments, the layer of a device comprises a material and the ink isdeposited onto the layer.

In certain embodiments, the ink is deposited in a predeterminedarrangement. For example, the ink can be deposited in a patterned orunpatterned arrangement.

It is believed that the present invention can offer significantadvantages, especially, for example, for devices including largesubstrates, e.g., larger than about 0.5 meters in at least one dimensionand/or when predetermined arrangements of nanomaterial are desired.

In certain embodiments and aspects of the inventions contemplated bythis disclosure, the nanomaterial comprises inorganic nanoparticlescapable of emitting light.

In certain embodiments and aspects of the inventions contemplated bythis disclosure, the nanomaterial comprises semiconductor nanocrystals.Semiconductor nanocrystals possess characteristics and properties thatmake them particularly well-suited for use in a variety of devices andother end-use applications, including, but not limited to, lightemitting devices, displays, photodetectors, nonvolatile random memorydevices, solar cells, sensors, photovoltaic devices, etc.

In certain embodiments and aspects of the inventions contemplated bythis disclosure, the nanomaterial comprises semiconductor nanocrystalswherein at least a portion of the semiconductor nanocrystals include oneor more ligands attached to a surface thereof.

In certain embodiments, a method further comprises removal of the liquidvehicle from the ink. In certain embodiments, the liquid vehicle isselected such that, upon removal of the liquid vehicle, the layerincluding the nanomaterial deposited thereon is planar.

In certain embodiments, the liquid vehicle comprises a liquid in whichthe material included in the layer onto which the ink is deposited isinsoluble.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a small molecule material. A “small molecule”material refers to any organic material that is not a polymer. A smallmolecule material can further include a metal. A small molecule caninclude an organometallic compound. A small molecule material caninclude a metal complex. A small molecule material can include repeatingunits in some circumstances. For example, using a long chain alkyl groupas a substituent does not remove a molecule from the “small molecule”class. Other examples of small molecule materials can include organicoligomer molecules (e.g., organic molecules of intermediate relativemolecular mass, the structure of which essentially comprises a smallplurality of units derived, actually or conceptually, from molecules oflower relative molecular mass, see “oligomer molecule” from IUPACCompendium of Chemical Terminology 2^(nd) Edition (1997) includingrelated Notes, which are hereby incorporated herein by reference.)

In certain embodiments, a small molecule material may serve as the coremoiety of a dendrimer, which includes a series of chemical shells builton the core moiety. The core moiety of a dendrimer may be a fluorescentor phosphorescent small molecule emitter.

Dendrimer substituents can also be used to enhance the ability of smallmolecules to undergo solution processing.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a polymer.

In certain embodiments, the layer of the device onto which the ink isdeposited can comprise an organic nanocrystal. Examples of organicnanocrystals include, without limitation, J-aggregates, H-aggregates,and organic nanocrystals including aggregates with other dipolearrangements. Examples of organic nanocrystals are described in S.Kirstein et al., “Herringbone Structures In Two-Dimensional SingleCrystals of Cyanine Dyes. I. Detailed Structure Analysis Using ElectronDiffraction”, J. Chem. Phys. 103(2) July 1995, pages 816 et seq.; S.Kirstein et al., “Herringbone Structures In Two-Dimensional SingleCrystals of Cyanine Dyes. II. Optical Properties”, J. Chem. Phys. 103(2)July 1995, pages 826 et seq.; A. Mishra et al. “Cyanines During the1990s: A Review”, Chem. Rev. 2000, 100, 1973-2011; and C. Peyratout etal., “Aggregation of Thiacyanine Derivatives On Polyelectrolytes: Phys.Chem. Chem. Phys., 2002, 4, 3032-3039, the disclosures of which arehereby incorporated herein by reference in their entireties.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises carbon nanotubes.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises a carbon nanotube/polymer blend or hybrid.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises an inorganic material.

In certain embodiments, the layer of the device onto which the ink isdeposited can be disposed over a substrate which may also include anelectrode.

In certain embodiments, the layer of the device onto which the ink isdeposited comprises an electrode.

In certain embodiments, one or more other layers can be disposed overthe substrate before the ink.

In certain embodiments, the method can further include depositing asecond electrode layer over the nanomaterial. The deposition of one ormore additional layers (including, for example, hole blocking layer,electron transport layer, electron injection layer, etc.) can alsooptionally be included before or after deposition of the secondelectrode layer. Passivation, packaging, etc. can also optionally beincluded.

In certain embodiments, the ink is deposited onto a material capable oftransporting charge.

In certain embodiments, the nanomaterial is deposited as one or moreseparate layers. In certain embodiments of fabricating a device,nanomaterial can be disposed between any two layers of the device. Incertain embodiments, nanomaterial comprising semiconductor nanocrystalscan be deposited as one or more separate emissive layers disposedbetween a hole transport layer and an electron transport layer. Incertain embodiments, for example, nanomaterial can be disposed betweentwo hole transport layers and/or between two electron transport layers.Each charge transport layer included in a device may further compriseone or more layers. As discussed elsewhere herein, other layers may alsobe included between the electron transport layers and the hole transportlayers. When included in the device as a separate layer, for example,nanomaterial comprising semiconductor nanocrystals can be disposed as acontinuous or substantially continuous thin film or layer. When disposedas a separate layer, the layer can be patterned or unpatterned.Preferably, the nanomaterial comprising semiconductor nanocrystalsincluded in the device comprises a substantially monodisperse populationof semiconductor nanocrystals.

In certain embodiments, nanomaterial comprising semiconductornanocrystals is deposited at a thickness of multiple monolayers or less.For example, the thickness can be greater than three monolayers, threeor less monolayers, two or less monolayers, a single monolayer, apartial monolayer, etc. The thickness of each deposited layer ofnanomaterial comprising semiconductor nanocrystals may vary. Preferably,the variation of the thickness at any point of the depositedsemiconductor nanocrystals is less than three monolayers, morepreferably less than two monolayers, and most preferably less than onemonolayer. When deposited as a single monolayer, preferably at leastabout 60% of the semiconductor nanocrystals are at single monolayerthickness, more preferably, at least about 80% of the semiconductornanocrystals are at single monolayer thickness, and most preferably, atleast about 90% of the semiconductor nanocrystals are at singlemonolayer thickness. In a light-emitting device, a monolayer can providethe beneficial light emission properties of semiconductor nanocrystalswhile minimizing the impact on electrical performance.

Semiconductor nanocrystals show strong quantum confinement effects thatcan be harnessed in designing bottom-up chemical approaches to createcomplex heterostructures with electronic and optical properties that aretunable with the size and composition of the semiconductor nanocrystals.

As discussed herein, in certain embodiments, nanomaterial comprisingsemiconductor nanocrystals can be deposited in a patterned arrangement.Patterned semiconductor nanocrystals can be used to form an array ofpixels comprising, e.g., red, green, and blue, or alternatively, red,orange, yellow, green, blue-green, blue, violet, or other visible,infrared, or ultraviolet emitting, or other combinations ofdistinguishable wavelength emitting pixels, that are energized toproduce light of a predetermined wavelength.

Generally, a device or array of devices capable of emitting a variety ofcolors includes a pattern of emissive materials capable of emittingdifferent colors. Depositing nanomaterials from inks in accordance withan embodiment of the present invention using inkjet printheads and/orother micro-dispensers allows such pattern to be deposited without theuse of shadow masks and other patterning techniques associated withvapor phase deposition. Such deposition process also eliminates the needfor a transfer step as in contact printing.

When deposited in a patterned arrangement, nanomaterial can be depositedin a pattern comprising features having at least one dimension at amicron-scale (e.g., less than 1 mm, less than 500 μm, less than 200 μm,less than 100 μm or less, less than 50 μm or less, less than 20 μm orless). Nanomaterial can also be deposited in a patterned arrangementcomprising features at greater than micron-scale.

A pattern comprising deposited nanomaterial having features on themicron scale may also be referred to herein as a micropattern. Amicropattern can have features on the micron scale, such as less than 1mm, less than 500 μm, less than 200 μm, less than 100 μm, less than 50μm, or 20 μm or less in size. A 20 μm feature size is sufficiently smallfor most light emitting devices and devices for other applications.

The surface on which the nanomaterial can be deposited can havedimensions of 1 cm or greater, 10 cm or greater, 100 cm or greater, or1,000 cm or greater.

Compositions and methods in accordance with the invention are scalableand can be useful in depositing a pattern comprising one or morenanomaterials over a wide range of surface areas.

For example, the method is useful for depositing nanomaterial over verysmall areas (for example, 100 μm catheters) to very large areas, (forexample, 12″ square areas). In further example, the method is alsouseful for depositing nanomaterial over surfaces with dimensions such asGEN2 (360 mm×465 mm), GEN3 (550 mm×650 mm), GEN3.5 (600 mm×720 mm), GEN4(730 mm×920 mm), GEN5 (1110 mm×1250 mm), GEN6 (1500 mm×1800 mm), GENT(1900 mm×2100 mm), and subsequent generations of glass that can be used,e.g., in displays. Optionally, areas onto which nanomaterial is appliedcan then be stitched (or tiled) together, to expand the printable areafrom 12″ squares, to ‘n×12″ squares’ as is frequently done in thesemiconductor lithography field.

Inks in accordance with the invention can be included in making variousdevices. Additional information concerning examples of various devicesand various deposition and other techniques that may be useful with thepresent invention include, for example, those disclosed in InternationalPatent Application No. PCT/US2007/014711 [Docket No. QDV00C1_PCT],entitled “Methods For Depositing Nanomaterial, Methods For Fabricating ADevice, And Methods For Fabricating An Array Of Devices”, of Seth A.Coe-Sullivan, filed 25 Jun. 2007, International Patent Application No.PCT/US2007/014705 [Docket No. QDV00C2_PCT], entitled “Methods ForDepositing Nanomaterial, Methods For Fabricating A Device, Methods ForFabricating An Array Of Devices And Compositions”, of Seth A.Coe-Sullivan, et al., filed 25 Jun. 2007, International PatentApplication No. PCT/US2007/014706 [Docket No. QDV00D2_PCT], entitled“Methods And Articles Including Nanomaterial”, of Seth A. Coe-Sullivan,et al., filed 25 Jun. 2007, International Patent Application No.PCT/US2007/08873, entitled “Composition Including Material, Methods OfDepositing Material, Articles Including Same And Systems For DepositingMaterial”, of Seth A. Coe-Sullivan, et al., filed 9 Apr. 2007,International Patent Application No. PCT/US2007/09255, entitled “MethodsOf Depositing Material, Methods Of Making A Device, And Systems AndArticles For Use In Depositing Material”, of Maria J, Anc, et al., filed13 Apr. 2007, International Patent Application No. PCT/US2007/08705,entitled “Methods And Articles Including Nanomaterial”, of SethCoe-Sullivan, et al, filed 9 Apr. 2007, International Patent ApplicationNo. PCT/US2007/08721, entitled “Methods Of Depositing Nanomaterial &Methods Of Making A Device” of Marshall Cox, et al., filed 9 Apr. 2007,U.S. patent application Ser. No. 11/253,612, entitled “Method And SystemFor Transferring A Patterned Material” of Seth Coe-Sullivan, et al.,filed 20 Oct. 2005, and U.S. patent application Ser. No. 11/253,595,entitled “Light Emitting Device Including Semiconductor Nanocrystals”,of Seth Coe-Sullivan, et al., filed 20 Oct. 2005, each of the foregoingpatent applications being hereby incorporated herein by reference.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix.

An example of an embodiment of a light-emitting device is shown in FIG.2. The depicted example includes a first electrode disposed over asubstrate, a first layer in electrical connection with the firstelectrode, a second layer in electrical connection with the first layer,and a second electrode in electrical connection with the second layer.The first layer can comprise a material capable of transporting holes(HTL) and the second layer can comprise a material capable oftransporting electrons (ETL). At least one layer can be non-polymeric.An emissive material is included between the two electrodes. Theemissive material can include a plurality of semiconductor nanocrystalsthat can be selected based upon their light-emissive characteristics(e.g., the wavelength of the photon emitted by the nanocrystal whenvoltage is applied across the device). The emissive material can beincluded as one (as shown in FIG. 2) or more layers between the firstlayer and the second layer. In the figures the layer including theemissive material is designated as a “quantum dot layer”. In theembodiment depicted in FIG. 2 the first electrode of the structure is incontact with the substrate. Each electrode can be connected to a powersupply to provide a voltage across the structure. Electroluminescencecan be produced by the semiconductor nanocrystals included in the devicewhen a voltage of proper polarity is applied across the heterostructure.

The device structure depicted in FIG. 2 maybe fabricated as follows. Asubstrate having a first electrode (e.g., an anode) disposed thereon maybe obtained or fabricated using any suitable technique. The firstelectrode may be patterned. A first layer (e.g., a hole transport layer)may be deposited using any suitable technique. An emissive layer isdeposited from an ink in accordance with an embodiment of the presentinvention. In certain embodiments, ink is dispensed from amicro-dispenser, e.g., inkjet printhead Inkjet printing is preferred,because it readily allows for the patterning of separate regions. Incertain embodiments, the liquid vehicle of the ink is selected suchthat, upon removal of the liquid vehicle, the layer(s) of the device areplanar (for example, utilizing a well structure such as typically usedin polymer light emitting device (PLED) technology). A second layer(e.g., an electron transport layer) may be deposited using any suitabletechnique. A second electrode (e.g., a cathode) may be deposited usingany suitable technique.

In the example shown in FIG. 2, light is emitted from the bottom of thestructure (through, e.g., ITO coated glass). If an adequately lighttransmissive top electrode is used, the structure could emit light fromthe top of the structure.

Alternatively, the structure of FIG. 2 can be inverted, in which caselight can be emitted from the top.

The simple layered structure illustrated in FIG. 2 is provided by way ofnon-limiting example, and it is understood that embodiments of theinvention may be used in connection with a wide variety of otherstructures. The specific materials and structures described herein areexemplary in nature, and other materials and structures may be used.Functional devices may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be limiting.

The color of the light output of a light-emitting device can beprecisely controlled by the selection of the composition, structure, andsize of the various semiconductor nanocrystals included in a device asthe emissive material. In certain embodiments, two or more differentsemiconductor nanocrystals (having different compositions, structures,and/or sizes) can be included.

FIG. 3 illustrates an example of another embodiment of a light-emittingdevice showing a glass substrate on which the device can be built and aprotective glass layer that can be used to encapsulate the device.

Optionally a desiccant or other moisture absorptive material can beincluded in the device before it is sealed, e.g., with an epoxy, such asa UV curable expoxy. Other desiccants or moisture absorptive materialscan be used.

The first electrode can be, for example, an anode comprising a high workfunction (e.g., great than 4.0 eV) hole-injecting conductor, such as anindium tin oxide (ITO) layer. Other anode materials include other highwork function hole-injection conductors including, but not limited to,for example, tungsten, nickel, cobalt, platinum, palladium and theiralloys, gallium indium tin oxide, zinc indium tin oxide, titaniumnitride, polyaniline, or other high work function hole-injectionconducting polymers. In certain embodiments, the first electrode islight transmissive or transparent. In addition to ITO, examples of otherlight-transmissive electrode materials include conducting polymers, andother metal oxides, low or high work function metals, conducting epoxyresins, or carbon nanotubes/polymer blends or hybrids that are at leastpartially light transmissive. An example of a conducting polymer thatcan be used as an electrode material is poly(ethlyendioxythiophene),sold by Bayer AG under the trade mark PEDOT. Other molecularly alteredpoly(thiophenes) are also conducting and could be used, as well asemaraldine salt form of polyaniline.

The second electrode can be, for example, a cathode comprising a lowwork function (e.g., less than 4.0 eV), electron-injecting, metal, suchas Al, Ba, Yb, Ca, a lithium-aluminum alloy (Li:Al), a magnesium-silveralloy (Mg:Ag), or lithium fluoride-aluminum (LiF:Al). The secondelectrode, such as Mg:Ag, can optionally be covered with an opaqueprotective metal layer, for example, a layer of Ag for protecting thecathode layer from atmospheric oxidation, or a relatively thin layer ofsubstantially transparent ITO. The second electrode can be sandwiched,sputtered, or evaporated onto the exposed surface of the solid layer.One or both of the electrodes can be patterned. The electrodes of thedevice can be connected to a voltage source by electrically conductivepathways. Upon application of the voltage, light is generated from thedevice.

In a device such as that shown in FIG. 2, for example, the firstelectrode can have a thickness of about 500 Angstroms to 4000 Angstroms.The first layer can have a thickness of about 30 Angstroms to about 1000Angstroms. The second layer can have a thickness of about 30 Angstromsto about 1000 Angstroms. The second electrode can have a thickness ofabout 5 Angstroms to greater than about 10,000 Angstroms.

Non-polymeric electrode materials can be deposited by, for example,sputtering or evaporating. Polymeric electrode materials can bedeposited by, for example, spin-casting.

As discussed above, the electrodes can be patterned. Electrode material,including light-transmittable electrode material, can be patterned by,for example, a chemical etching method such as a photolithography or aphysical etching method using laser, etc. Also, the electrode may bepatterned by vacuum vapor deposition, sputtering, etc. while masking.

Hole transport and electron transport layers can be collectivelyreferred to as charge transport layers. Either or both of these layerscan comprise organic or inorganic materials. Examples of inorganicmaterial include, for example, inorganic semiconductors. The inorganicmaterial can be amorphous or polycrystalline. An organic chargetransport material can be polymeric or non-polymeric. In certainembodiments, the charge transport materials are gradient sublimationpurified.

An example of a typical organic material that can be included in anelectron transport layer includes a molecular matrix. The molecularmatrix can be non-polymeric. The molecular matrix can include a smallmolecule, for example, a metal complex. The metal complex of8-hydoxyquinoline can be an aluminum, gallium, indium, zinc or magnesiumcomplex, for example, aluminum tris(8-hydroxyquinoline) (Alq₃). Otherclasses of materials in the electron transport layer can include metalthioxinoid compounds, oxadiazole metal chelates, triazoles,sexithiophenes derivatives, pyrazine, and styrylanthracene derivatives.Balq2 is an example of another material that can be included in anelectron transport layer. An electron transport layer comprising anorganic material may be intrinsic (undoped) or doped. Doping may be usedto enhance conductivity. See, for example, U.S. Provisional PatentApplication No. 60/795,420 of Beatty et al, for “Device IncludingSemiconductor Nanocrystals And A Layer Including A Doped OrganicMaterial And Methods”, filed 27 Apr. 2006, which is hereby incorporatedherein by reference in its entirety.

An example of a typical organic material that can be included in a holetransport layer includes an organic chromophore. The organic chromophorecan include a phenyl amine, such as, for example,N,N′-diphenyl-N,N′-bis(3-mehtylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TPD). Other hole transport layer can includeN,N′-bis(3-methylphenyl)-N,N-bis(phenyl)-spino (spiro-TPD),4-4′-N,N′-dicarbazolyl-biphenyl (CBP),4,4-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD), etc., apolyaniline, a polypyrrole, a poly(phenylene vinylene), copperphthalocyanine, an aromatic tertiary amine or polynuclear aromatictertiary amine, a 4,4′-bis(p-carbazolyl)-1,1′-biphenyl compound, or anN,N,N′,N′-tetraarylbenzidine. A hole transport layer comprising anorganic material may be intrinsic (undoped) or doped. Doping may be usedto enhance conductivity. Examples of doped hole transport layers aredescribed in U.S. Provisional Patent Application No. 60/795,420 ofBeatty et al, for “Device Including Semiconductor Nanocrystals And ALayer Including A Doped Organic Material And Methods”, filed 27 Apr.2006, which is hereby incorporated herein by reference in its entirety.

Charge transport layers comprising organic materials and otherinformation related to fabrication of organic charge transport layers,light-emitting devices, and related technology are discussed in moredetail in U.S. patent application Ser. No. 11/253,612 for “Method AndSystem For Transferring A Patterned Material”, filed 21 Oct. 2005, andSer. No. 11/253,595 for “Light Emitting Device Including SemiconductorNanocrystals”, filed 21 Oct. 2005 and International Patent ApplicationNo. PCT/US2007/13152 for “Light-Emitting Devices And Displays WithImproved Performance”, filed 4 Jun. 2007. The foregoing patentapplications are hereby incorporated herein by reference in itsentirety.

Organic charge transport layers may be disposed by known methods such asa vacuum vapor deposition method, a sputtering method, a dip-coatingmethod, a spin-coating method, a casting method, a bar-coating method, aroll-coating method, and other film deposition methods. In certainembodiments, organic layers are deposited under ultra-high vacuum (e.g.,<10⁻⁸ torr), high vacuum (e.g., from about 10⁻⁸ torr to about 10⁻⁵torr), or low vacuum conditions (e.g., from about 10⁻⁵ torr to about10⁻³ torr). Preferably, the organic layers are deposited at high vacuumconditions of from about 1×10⁻⁷ to about 1×10⁻⁶ torr or from about1×10⁻⁷ to about 5×10⁻⁶ torr. Alternatively, organic layers may be formedby multi-layer coating while appropriately selecting solvent for eachlayer.

Charge transport layers including inorganic materials and otherinformation related to fabrication of inorganic charge transport layersare discussed further below and in more detail in U.S. PatentApplication No. 60/653,094 for “Light Emitting Device IncludingSemiconductor Nanocrystals, filed 16 Feb. 2005 and U.S. patentapplication Ser. No. 11/354,185, filed 15 Feb. 2006, the disclosures ofeach of which are hereby incorporated herein by reference in theirentireties.

Charge transport layers comprising an inorganic semiconductor can bedeposited on a substrate at a low temperature, for example, by a knownmethod, such as a vacuum vapor deposition method, an ion-plating method,sputtering, inkjet printing, etc.

The substrate can be opaque, light transmissive, or transparent. Thesubstrate can be rigid or flexible. The substrate can be plastic, metalor glass.

In some applications, the substrate can include a backplane. Thebackplane includes active or passive electronics for controlling orswitching power to individual pixels. Including a backplane can beuseful for applications such as displays, sensors, or imagers. Inparticular, the backplane can be configured as an active matrix, passivematrix, fixed format, direct drive, or hybrid. The display can beconfigured for still images, moving images, or lighting. A displayincluding an array of light emitting devices can provide white light,monochrome light, or color-tunable light.

In addition to the charge transport layers, a device may optionallyfurther include one or more charge-injection layers, e.g., ahole-injection layer (HIL) (either as a separate layer or as part of thehole transport layer) and/or an electron-injection layer (EIL) (eitheras a separate layer as part of the electron transport layer). Chargeinjection layers comprising organic materials can be intrinsic(un-doped) or doped. See, for example, U.S. Provisional PatentApplication No. 60/795,420 of Beatty et al, for “Device IncludingSemiconductor Nanocrystals And A Layer Including A Doped OrganicMaterial And Methods”, filed 27 Apr. 2006, which is hereby incorporatedherein by reference in its entirety.

One or more charge blocking layers may still further optionally beincluded. For example, an electron blocking layer (EBL), a hole blockinglayer (HBL), or an exciton blocking layer (eBL), can be introduced inthe structure. A blocking layer can include, for example,3-(4-biphenylyl)-4-phenyl-5-tert butylphenyl-1,2,4-triazole (TAZ),2,2′,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TBPi),3,4,5-triphenyl-1,2,4-triazole,3,5-bis(4-tert-butylphenyl)-4-phenyl-1,2,4-triazole, bathocuproine(BCP), 4,4′,4″-tris {N-(3-methylphenyl)-Nphenylamino}triphenylamine(m-MTDATA), polyethylene dioxythiophene (PEDOT),1,3-bis(5-(4-diphenylamino)phenyl-1,3,4-oxadiazol-2-yl)benzene,2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,4-oxadiazole,1,3-bis[5-(4-(1,1-dimethylethyl)phenyl)-1,3,4-oxadiazol-5,2-yl)benzene,1,4-bis(5-(4-diphenylamino)phenyl-1,3,4-oxadiazol-2-yl)benzene, or1,3,5-tris[5-(4-(1,1-dimethylethyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene.Charge blocking layers comprising organic materials can be intrinsic(un-doped) or doped. See, for example, U.S. Provisional PatentApplication No. 60/795,420 of Beatty et al, for “Device IncludingSemiconductor Nanocrystals And A Layer Including A Doped OrganicMaterial And Methods”, filed 27 Apr. 2006, which is hereby incorporatedherein by reference in its entirety.

The charge injection layers (if any), and charge blocking layers (ifany) can be deposited on a surface of one of the electrodes by spincoating, dip coating, vapor deposition, or other thin film depositionmethods. See, for example, M. C. Schlamp, et al., J. Appl. Phys., 82,5837-5842, (1997); V. Santhanam, et al., Langmuir, 19, 7881-7887,(2003); and X. Lin, et al., J. Phys. Chem. B, 105, 3353-3357, (2001),each of which is incorporated by reference in its entirety.

Other multilayer structures may optionally be used to improve theperformance (see, for example, U.S. patent application Ser. Nos.10/400,907 and 10/400,908, filed Mar. 28, 2003, each of which isincorporated by reference in its entirety) of the light-emitting devicesand displays of the invention. The performance of light-emitting devicescan be improved by increasing their efficiency, narrowing or broadeningtheir emission spectra, or polarizing their emission. See, for example,Bulovic et al., Semiconductors and Semimetals 64, 255 (2000), Adachi etal., Appl. Phys. Lett. 78, 1622 (2001), Yamasaki et al., Appl. Phys.Lett. 76, 1243 (2000), Dirr et al., Jpn. J. Appl. Phys. 37, 1457 (1998),and D'Andrade et al., MRS Fall Meeting, BB6.2 (2001), each of which isincorporated herein by reference in its entirety.

Preferably, a device including a nanomaterial comprising semiconductornanocrystals is processed in a controlled (oxygen-free andmoisture-free) environment, preventing the quenching of luminescentefficiency during the fabrication process.

Besides being useful to deposit nanomaterials in fabricating devices anddisplays, other layers of a device and/or array (e.g., electrodes,charge transport layers, charge blocking layers, charge injectionlayers, etc.) can also be deposited from micro-dispensers, e.g., inkjetprintheads. Fabricating multiple device layers using micro-dispensers,e.g., inkjet printheads, can simplify the manufacturing process andprovide other manufacturing efficiencies.

Because of the diversity of semiconductor nanocrystal materials that canbe prepared, and the wavelength tuning via semiconductor nanocrystalcomposition, structure, and size, devices that can emit light of apredetermined color are possible with use of semiconductor nanocrystalsas the emissive material. Semiconductor nanocrystal light-emitteddevices can be tuned to emit anywhere in the spectrum. Light-emittingdevices can be prepared that emit visible or invisible (e.g., IR) light.The size and material of a semiconductor nanocrystal can be selectedsuch that the semiconductor nanocrystal emits light having apredetermined wavelength. Light emission can be of a predeterminedwavelength in any region of the spectrum, e.g., visible, infrared, etc.For example, the wavelength can be between 300 and 2,500 nm or greater,for instance between 300 and 400 nm, between 400 and 700 nm, between 700and 1100 nm, between 1100 and 2500 nm, or greater than 2500 nm.

In certain embodiments, individual light-emitting devices can be formed.In other embodiments, a plurality of individual light-emitting devicescan be formed at multiple locations on a single substrate to form adisplay.

A display can include two or more devices that emit at the same ordifferent wavelengths. By patterning the substrate with arrays ofnanomaterials comprising different color-emitting semiconductornanocrystals, a display including pixels of different colors can beformed. Patterned semiconductor nanocrystals can be used to form anarray of pixels comprising, e.g., red, green, and blue or alternatively,red, yellow, green, blue-green, and/or blue emitting, or othercombinations of distinguishable color emitting pixels, that areenergized to produce light of a predetermined wavelength. In certainembodiments, one or more pixel can emit in the ultraviolet or infraredemission portion of the spectrum.

An individual light-emitting device or one or more light-emittingdevices of a display can optionally include a mixture of differentcolor-emitting semiconductor nanocrystals formulated to produce a whitelight. White light can alternatively be produced from a device includingred, green, blue, and, optionally, additional pixels.

Examples of other displays are included in U.S. Patent Application No.60/771,643 for “Displays Including Semiconductor Nanocrystals AndMethods Of Making Same”, of Seth Coe-Sullivan et al., filed 9 Feb. 2006,the disclosure of which is hereby incorporated herein by reference inits entirety.

As discussed above, the methods described herein may have applicationsin fabricating other devices in addition to light-emitting devices,including, but not limited to, solar cells, photovoltaic devices,photodetectors, non-volatile memory devices, etc.

For example, a nanomaterial, e.g., a nanomaterial comprisingsemiconductor nanocrystals, can be deposited by a method in accordancewith the invention in fabrication of a photodetector device or array ofphotodetector devices. A photodetector device includes one or morenanomaterials comprising a plurality of semiconductor nanocrystals whichare selected based upon absorption properties. When included in aphotodetector, semiconductor nanocrystals are engineered to produce apredetermined electrical response upon absorption of a particularwavelength, typically in the IR or MIR region of the spectrum. Examplesof photodetector devices including semiconductor nanocrystals aredescribed in “A Quantum Dot Heterojunction Photodetector” by AlexiCosmos Arango, Submitted to the Department of Electrical Engineering andComputer Science, in partial fulfillment of the requirements for thedegree of Masters of Science in Computer Science and Engineering at theMassachusetts Institute of Technology, February 2005, the disclosure ofwhich is hereby incorporated herein by reference in its entirety. One ormore photodetectors can further be included in an imaging device, suchas an hyperspectral imaging device. See, for example, U.S. ProvisionalApplication No. 60/785,786 of Coe-Sullivan et al. for “HyperspectralImaging Device”, filed 24 Mar. 2006, the disclosure of which is herebyincorporated herein by reference in its entirety.

In one embodiment, a method of fabricating a photodetector deviceincludes depositing an in accordance with the an embodiment of thepresent invention onto a layer of the device from a micro-dispenser. Inone embodiment, the nanomaterial comprises semiconductor nanocrystals.The ink can be deposited onto the layer of the device in a predeterminedpatterned arrangement or as an unpatterned arrangement, including, onlyby way of example, a layer, a continuous film, etc. Preferably theliquid vehicle is removed from the deposited ink before deposition ofany other material or layer thereover.

In another embodiment, a method of fabricating an array of photodetectordevices includes depositing an ink in accordance with an embodiment ofthe invention onto a layer of the device from a micro-dispenser. In oneembodiment, the nanomaterial comprises semiconductor nanocrystals. Theink comprising a nanomaterial and a liquid vehicle can be deposited onthe device layer in a predetermined arrangement (patterned orunpatterned). The device layer can be disposed on a substrate thatfurther includes an electrode. A second electrode can be deposited overthe deposited nanomaterial, preferably after removal of the liquidvehicle from the ink. In one embodiment, the device layer onto which thenanomaterial is deposited comprises a charge transport material.Optionally, a second charge transport layer can be formed between thenanomaterial layer and the second electrode.

A method of fabricating a photodetector device or array of devices canoptionally include depositing one or more nanomaterials in apredetermined arrangement (patterned or unpatterned). As discussedabove, an ink including a nanomaterial and a liquid vehicle is depositedfrom a micro-dispenser.

Methods in accordance with the invention can also be used in depositionnanomaterials in the fabrication of memory devices. An example of anonvolatile device is described in U.S. patent application Ser. No.10/958,659, for “Non-Volatile Memory Device”, of Bawendi et al., filed 6Oct. 2004, the disclosure of which is hereby incorporated herein byreference in its entirety.

For additional information relating to semiconductor nanocrystals andtheir use, see also U.S. Patent Application No. 60/620,967, filed Oct.22, 2004, and Ser. No. 11/032,163, filed Jan. 11, 2005, U.S. patentapplication Ser. No. 11/071,244, filed 4 Mar. 2005. Each of theforegoing patent applications is hereby incorporated herein by referencein its entirety.

As used herein, “top” and “bottom” are relative positional terms, basedupon a location from a reference point. More particularly, “top” meansfurthest away from the substrate, while “bottom” means closest to thesubstrate. For example, for a light-emitting device that optionallyincludes two electrodes, the bottom electrode is the electrode closestto the substrate, and is generally the first electrode fabricated; thetop electrode is the electrode that is more remote from the substrate,on the top side of the light-emitting material. The bottom electrode hastwo surfaces, a bottom surface closest to the substrate, and a topsurface further away from the substrate. Where, e.g., a first layer isdescribed as disposed or deposited “over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is otherwise specified.For example, a cathode may be described as “disposed over” an anode,even though there are various organic and/or inorganic layers inbetween.

As used herein, the singular forms “a”, “an” and “the” include pluralunless the context clearly dictates otherwise. Thus, for example,reference to a nanomaterial includes reference to one or more of suchmaterials.

All the patents and publications mentioned above and throughout areincorporated in their entirety by reference herein. Further, when anamount, concentration, or other value or parameter is given as either arange, preferred range, or a list of upper preferable values and lowerpreferable values, this is to be understood as specifically disclosingall ranges formed from any pair of any upper range limit or preferredvalue and any lower range limit or preferred value, regardless ofwhether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1. An ink composition comprising: a light emissive nanomaterialcomprising a plurality of quantum confined semiconductor nanocrystalscapable or emitting light, a plurality of scattering particles, and aliquid vehicle comprising a non-polar organic solvent.
 2. An inkcomposition in accordance with claim 1 wherein the scattering particlescomprise metal or metal oxide particles, air bubbles, solid glass beads,or hollow glass beads.
 3. An ink composition in accordance with claim 1wherein the scattering particles comprise TiO₂, SiO₂, BaTiO₃, and ZnO.4. An ink composition in accordance with claim 1 wherein at least aportion of the scattering particles have a spherical shape.
 5. An inkcomposition in accordance with claim 1 wherein the scattering particleshave a spherical shape.
 6. An ink composition in accordance with claim 1wherein at least a portion of the scattering particles include asurface-treatment to improve dispersability and stability in the liquidmedium.
 7. An ink composition in accordance with claim 1 wherein thescattering particles comprise comprises particles of TiO₂ with anaverage particle size of 0.2 μm.
 8. An ink composition in accordancewith claim 1 wherein the concentration of scattering particles is in arange from 0.001% and 20% by weight.
 9. An ink composition in accordancewith claim 1 wherein the concentration of scattering particles is in arange from 0.1% and 10% by weight.
 10. An ink composition in accordancewith claim 1 wherein the concentration of scattering particles is in arange from 0.1% and 3% by weight.
 11. An ink composition in accordancewith claim 1 wherein the ink composition includes at least about 0.1 mgof quantum confined semiconductor nanocrystals per ml of liquid vehicle.12. An ink composition in accordance with claim 1 wherein the inkcomposition includes at least about 1 mg of quantum confinedsemiconductor nanocrystals per ml of liquid vehicle.
 13. An inkcomposition in accordance with claim 1 wherein the ink compositionincludes at least about 5 mg of quantum confined semiconductornanocrystals per ml of liquid vehicle.
 14. An ink composition inaccordance with claim 1 wherein the ink composition includes at leastabout 10 mg of quantum confined semiconductor nanocrystals per ml ofliquid vehicle.
 15. An ink composition in accordance with claim 1wherein the ink composition includes at least about 25 mg of quantumconfined semiconductor nanocrystals per ml of liquid vehicle.
 16. An inkcomposition in accordance with claim 1 wherein the ink compositionincludes at least about 50 mg of quantum confined semiconductornanocrystals per ml of liquid vehicle.
 17. An ink composition inaccordance with claim 1 wherein at least a portion of the quantumconfined semiconductor nanocrystals comprise a core/shell structure. 18.An ink composition in accordance with claim 1 wherein the inkcomposition comprises a dispersion.
 19. An ink composition in accordancewith claim 1 wherein the ink composition comprises a colloidaldispersion. 20-39. (canceled)
 40. A device comprising a including acomposition in accordance with claim
 1. 41-46. (canceled)